Activate numerical tests & add an erratic test

[godotalgorithm]

I'm activating numerical tests on heat of formation outputs, which should have tighter tolerances than other outputs. I have a relatively loose tolerance to start with, and I may have to add precision keywords to tighten up a few of the more sensitive tests. Also, Jimmy reported a bug recently that I haven't been able to reliably reproduce, so I'm adding it to the erratic tests for now.

Status

• [ ] Ready for merge

[godotalgorithm]

The numerical error threshold is adjustable so that it is not a barrier against adding new tests.